Cathodically depositable electrocoating lacquer baths used in industrial applications are operated at bath solids contents of generally between 10 and 25 wt. %. The solvent content thereof should be as low as possible.
It is known for users to prepare or make good the solids content of electrocoating lacquer baths using single-component concentrates. These concentrates are produced by grinding the pigments and extenders in the organic solution of a cathodic electrocoating lacquer binder, neutralisation with acid and, generally, dilution with water. The concentrates contain little or no water and are generally completely neutralised. They are usually supplied to users at a solids content of above 50 wt. % and a solvent content of between 20 and 40 wt. %. The concentrates are stable in storage, i.e. they do not require constant mixing, for example by stirring. The concentrates have elevated viscosities of, for example, above 2000 mPa.cndot.s at 20.degree. C. When a cathodic electrocoating lacquer bath is first prepared, the user must mix them with water or, if the solids content is to be made good, with solids-depleted cathodic electrocoating lacquer bath contents. As a consequence of the great differences in viscosity, this requires specific technical equipment and methods and is highly labour intensive. These single-component concentrates are thus conveyed from the delivery containers using pumps suitable for thick materials and prediluted in continuously or discontinuously operated premixing apparatus to a solids content of generally below 30 wt. %. If immobile, for example if unstirred, these premixes are either not stable in storage or stable for only a short period; they may be further diluted without any particular effort to yield the finished cathodic electrocoating lacquer bath. The finished cathodic electrocoating lacquer baths produced in this manner have undesirably high solvent contents of, for example, above 4 wt. % at a bath solids content of 20 wt. %. This corresponds to an organic solvent content of 20 to 50 wt. %, relative to the solids content of the cathodic electrocoating baths.
Alternatively, two-component cathodic electrocoating lacquer materials have been developed from which users may first prepare cathodic electrocoating lacquer baths by dilution with water or with which solids content may be made good by mixing with solids-depleted cathodic electrocoating lacquer bath contents (c.f. EP-A-0 183 025, EP-A-0 203 024 and H. Kittel, Lehrbuch der Lacke und Beschichtungen, volume 7, Verlag W. A. Colomb, Berlin, 1979, page 166). The two-component cathodic electrocoating lacquer materials are a) a binder component in the form of a solvent-free or low-solvent, aqueous dispersion of the cathodic electrocoating lacquer binder and any optionally present crosslinking agent (cathodic electrocoating lacquer dispersion) and b) a separate pigment paste, which is generally produced by grinding the pigments and extenders in a special paste resin. Both components are stable in storage even without stirring and, by virtue of their low viscosity of generally below 500 mPa.cndot.s measured by rotational viscosimetry at 20.degree. C. and a shear gradient of 150 s.sup.-1, may be handled by users without requiring any particular equipment. Both components are compatible with the cathodic electrocoating lacquer bath contents, while directly mixing the two components together generally gives rise to incompatibilities and/or stability problems, frequently after only brief storage. Dilution with water or with solids-depleted cathodic electrocoating lacquer bath contents is thus performed separately, for example by separate or parallel apportionment into the solids-depleted cathodic electrocoating lacquer bath. In order to maintain constant deposition characteristics and lacquer film parameters, the user must apportion the two components at a fixed ratio one to the other to the cathodic electrocoating lacquer bath, so entailing the possibility of errors. Logistical requirements are greater than working with a single-component material, for example storage is more costly and the user's testing costs are multiplied. Cathodic electrocoating lacquer baths produced on the basis of two-component cathodic electrocoating lacquer materials have a low organic solvent content of, for example, below 4 wt. % at a bath solids content of 20 wt. %, corresponding to a solvent content of 0 to 20 wt. %, relative to the bath solids content.
The object arose of providing a single-component concentrate which is suitable for producing and making good the solids content of opaquely pigmented, cathodically depositable electrocoating lacquer baths containing no or little solvent, which is stable in storage in the immobile state and may be handled simply by users. It should not entail any elaborate logistics.